In mammals the rejection of allografts is primarily accomplished by cell-mediated immunity including T cells. Recently, considerable studies reveal the existence of helper and cytotoxic T cell subsets in fish. Here we investigate the kinetics of CD4(+) and CD8 alpha(+) T cells along with sIgM(+) cells and phagocytic cells in an allogeneic scale graft model using ginbuna crucian carp for understanding the mechanisms of cell-mediated immune response. The results showed that CD4(+) T cells first infiltrated into allogeneic scales followed by CD8 alpha(+) and sIgM(+) cells, and finally phagocytic cells appeared in the graft. Furthermore, most of the CD8 alpha(+) T cells appeared on the border of the allografted scales at the time of rejection. These results suggest that T cells play crucial roles and work together with other cell types for completion of allograft rejection. (C) 2015 Elsevier Ltd. All rights reserved.